- This topic has 36 replies, 5 voices, and was last updated 19 years, 1 month ago by
Bruce R. Schaefer.
Bruce R. Schaefer.-
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Doug Gerrard
This weekend I tested the ejection charges for Freeze Frame. You can see the video’s at http://www.rocketryphotography.com/rockets/RocketsFreezeframe.html but I have to warn you they are over 10M each.
The reason why I say nothing beats ground testing is that for the apogee charge, the calculations were just about right, 0.5 gms for the given size of the space. BUT the 5″ tube length also had an additional 9″ of coupler to move.
The main charge calculated to be 3 gms but I decided to try 2 gms just in case. It nearly put a hole in the wall!!! In either case the charge was just barely suppose to shear the four 4-40 screws but they had PLENTY of power to do that and more.
Bottom line, DO the Ground Test. It is worth it.
Doug
Anonymous
Doug, that is solid advice. The online calculators are a decent STARTING point, but that is it. I’d never dream of flying a bird w/o a ground test first — unless I had a very, very similar rocket that I could cross reference.
Our “O” project will definitely have a lot of ground testing. It is just senseless to risk something that entails so much work.
I’m quite often surprised when I ground test– sometimes it takes a lot less powder than I expected, and sometimes a lot more than anticipated. That is why I tend to test all the time.
Incidentally, on smaller charges– the type of ematch will definitely affect things. In other words, an Oxral w/ 0.5g is often way different than a Davey 28BR w/ 0.5g of the same powder. If you change ematches, re-do your ground tests when using less than about 1g of powder. On bigger charges, the effect of a different brand of ematch is minimal.
JW
Conway Stevens
Thats interesting on the ematch differences there. Any Idea why? Has anyone used the quickburst ematches yet?
Doug Gerrard
My tests were done with Quickburst. Mostly because I have a hard time finding any others.
Doug
Anonymous
Thats interesting on the ematch differences there. Any Idea why? Has anyone used the quickburst ematches yet?
The reason is because some of the ematches have differing amounts of pyrogen. IIRC, the difference between a 28B and a 28BR is that one of them has 3X the pyrogen vs. the other. On a some of my rockets I use 0.25g. I’ll bet the ematch has that much oomph.
There is a very clear difference between ematches — no doubt about it. Not a problem, though– just test, and record your ematch and your charge and go from there.
The reason it is not a factor on a 4g charge is because the BP/Pyrogen ratio is way up there. If the ematch = 0.25g or 0.5g of energy, that pales in comparison to 4g of FFFF. OTOH, if you aren’t using that much powder, say 0.25g, then your ematch is (potentially) doing some of the work.
JW
Conway Stevens
Doug as all of my experince has been on Davey Fires or Oxral how did you like the Quickburst?
Doug Gerrard
I always like Davey Fires but as I mentioned I just can’t find them anywhere. I picked up Quickburst at LDRS and they are in just about everyway comparable to Davey Fires. They list their spec on the package (and probably their web site) and I have tested nearly a dozen so far (all on the ground) and they have all worked. So far, I can’t say anything bad about them except one little thing.
When I bought them I wanted the 2m lengths and the guy thought I was strange for wanting such a long igniter. They have only 3 foot leads. So for your M’s and other long applications, you get to solder used leads to make them the length you need. BTW, when I asked about getting them he said he couldn’t get any that long, if you believe that. The only other item maybe worth mentioning is that the lead also seem to be smaller than Davey fire but I don’t know what gauge wire it is.
Bottom line is, I’m using them in Freeze Frame, which requires eleven of them per flight including the motor ignitors.
Doug
Conway Stevens
Cool Doug. Thanks for the info. I bought a box of 100 of the Quickburst and they do look very simular to Davey’s. But I to wish I could get the long 3m length. I use the left over wires for my ignitors as well. I know tons of people that like them for that very reason. I was mainly concerned with the rekiabillity and quality was all. Want to be able to have some faith or trust that my chrges will work when I do my L3 cert.
Once again Doug Thanks again. And boy I cant wait to see your set up.
Bruce R. Schaefer
I’m going to use, and ground test first but haven’t yet, the Quickburst 1-12gm. canisters for my L3. Heard very good things about them. I’ll probably test at a launch, since I don’t want to shoot anything through my fence. 🙂 This is a great and needed post.
Conway Stevens
Actually when I ground test I do a net/catch assembly with a large blanket or 2. keeps it from going throug the fence. And I have tested up to 7 to 8 grams before.
Doug Gerrard
Anonymous
Conway Stevens
Bruce R. Schaefer
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